Dec. 29, 2011 -- Strokes so tiny they are termed ''silent'' may be linked to memory loss in older adults.
Previously, experts thought that memory loss among older adults was caused by deterioration in the hippocampus, the part of the brain involved in memory and other functions. Although that is still true, study researcher Adam Brickman, PhD, says his new research adds another possible cause to the list.
"What our study suggests is, even when we account for the decline in memory attributed to hippocampal shrinkage or degeneration, that strokes ... play an additional role in the memory decline," Brickman says. He is the Herbert Irving assistant professor of neuropsychology at Columbia University College of Physicians and Surgeons.
Typically, he says, stroke has been linked to loss of mental abilities such as how fast we process information or attention, but not necessarily memory.
The new research is published online in the journal Neurology.
Strokes and Memory: The Possible 'Silent' Link
The researchers tested 658 people. All were age 65 or older and free of dementia. They gave them MRI brain scans. They also tested them on memory, language, speed at processing information, and visual perception.
The men and women were enrolled in a larger study of aging and dementia. All live in northern Manhattan.
The researchers looked at the MRIs for evidence of these tiny strokes and counted them. "These are strokes for the most part that people didn't realize they had," Brickman says. "On an MRI, it's like a dark hole that indicates some tissue loss due to vascular injury." Vascular injury refers to blood vessel damage.
To evaluate shrinkage, the researchers identified the hippocampus on the MRI and manually measured it.
Silent strokes were found in 174 people.
Those who had the silent strokes scored worse on memory tests than did those who did not.
The silent strokes also were linked with a smaller hippocampus size. Smaller hippocampus size, by itself, was also linked with poorer memory.
But the link between stroke and memory loss was found regardless of the size of the hippocampus.
The study was supported by the National Institutes of Health. Brickman serves as a consultant for ProPhase LLC, a firm involved in applied measurement for clinical and pharmaceutical research. Other co-authors report serving as consultants for Pfizer, Merck Serono, GlaxoSmithKline, and other drug companies.
Strokes and Memory: Perspective
"Given the near universal interest in preserving cognitive function in late life, and the epidemic of fear of Alzheimer's disease, these findings suggest possible approaches to early identification and prevention," says Richard B. Lipton, MD, director of the division of cognitive aging and dementia at Albert Einstein College of Medicine.
"Broadly, these findings, along with the findings of others, suggest that modifying cardiovascular risk factors and preventing stroke may contribute to the prevention of memory decline and perhaps delay or prevent the onset of dementia."
Neelum T. Aggarwal, MD, co-leader of the Rush University Medical Center's Alzheimer's Disease Research Center's Clinical Core and associate professor of neurological sciences, agrees. She reviewed the findings.
Doctors should aggressively manage vascular risk factors such as high blood pressure to prevent cognitive decline, she says.
Research in the area is ongoing, Lipton says.
Strokes and Memory: What to Do
"What we are showing over and over is the significant contribution of vascular disease to cognitive function in older adults," Brickman says. The silent strokes are potentially preventable, he says.
Doctors should consider ordering an MRI for older adults with substantial vascular risk factors such as diabetes or high blood pressure, Brickman says.